Tanks, sewers, and other enclosures that must be entered periodically require some type of air ventilation system for the men working in the enclosure. Without some type of air ventilation the workers would be required to wear respirators. The current apparatus used today normally includes an air pump outside the enclosure and an 8-inch flexible hose leading into the enclosure. The normal 24 inch manhole is barely large enough to allow a person to enter the enclosure with tools and/or materials. When an 8-inch hose is also in the manhole it may prevent such a person from entering the enclosure, and it always provides an obstruction that tends to catch tools on the man's belt with the possibility of damaging the hose or dropping tools on a worker already in the enclosures.
It is an object of this invention to provide an improved air conduit for ventilating an enclosure with a manhole entrance. It is another object of this invention to provide such an air conduit which is flattened in the area where it passes through the manhole. Still other objects will appear in the more detailed description which follows.